Field of the Invention
The present invention is generally concerned with a method and device for selecting information usable by a local unit connected to a digital transmission system, in which the selection criterion is part of the message transmitted and is located at the start of the message.
It applies, for example, to the sorting of digital information received sequentially over one or more independent transmission lines and organized in time in such a way that the information needed for selection purposes is known before the information proper so that sorting can be carried out before the end of transmission of the current message on the channel in question.
The invention is more particularly, although not exclusively, directed to a device of this kind implemented in the form of a highly integrated interface unit between a processor and one or more serial transmission lines conveying information in the form of a succession of words each representing a predetermined frame, in accordance with the aeronautical standard ARINC 429, for example.
According to this standard, each 32-bit word comprises in succession:
a first number on eight bits (bits 0 through 7) defining a label; PA0 a second number (SDI) on two bits (bits 8 and 9) identifying the source or the destination of the word; PA0 a third number on 21 bits (bits 10 through 30) containing the transmitted data; and PA0 a parity bit (bit 31). PA0 the maximum and minimum times associated with the transmission of an information bit; PA0 the duty factor of the modulation signal; PA0 the time interval or "Gap" between two words; PA0 the number of bits per word (32 in this instance); and PA0 the parity of the words. PA0 cyclical scanning at a fixed frequency of a programmed list of conditions in memory; PA0 simultaneous acquisition of information on said channels; PA0 activation of a selection process each time that the selection information of a message received on either channel has been acquired, the selection process including a synchronization stage which waits for the scanning process to cross the start of the list of conditions, a comparison (pattern matching) sequence on the selection information contained in the message being received, and the production of a selection variable which indicates if the message being received is of interest to the local unit or not, the selection process ending either when all the conditions from the list have been exhausted and on returning to the start of list condition or upon reading a special end of list code; PA0 the memorization of messages selected in a buffer accessible to the local unit. PA0 a receive unit connected to at least one transmission line by a demodulator and comprising a buffer; PA0 an interface to the local unit; PA0 a first random access memory associated with a data management circuit; PA0 a pattern matching message recognition device looking for coincidence between the selection criteria of the words being received on both channels and the label trap code bits stored in an area of a second random access memory, the codes being presented sequentially by a label trap pointer; PA0 a control unit driving an address generator associated with the second random access memory through a receive pointer, a send pointer and a condition list pointer.
The standard naturally imposes a number of conditions (called "templates"), in particular with regard to:
In this type of application the invention proposes to carry out before each word is transmitted sorting relating not only to the conformity of the word to the previously listed templates but also to the pertinence of this word for the processor, without using any external personalizing memories.